Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eye sight.
Types of Equine Keratitis
Superficial keratitis is common in all species and is characterized by corneal vascularization and opacification, which may be due to edema, cellular infiltrates, pigmentation, or fibroplasia. If ulceration is present, pain—manifest by epiphora and blepharospasm—is an outstanding sign. Unilateral keratitis frequently is traumatic in origin. Mechanical factors, such as lid conformational defects and foreign bodies, should always be eliminated as possible causes because improvement will not occur until they are resolved. Ulcerative keratitis may be complicated by secondary invasion by bacteria and, in horses, by saprophytic fungi. Bilateral superficial keratitis may be immune-mediated or associated with a lack of tears, eyelid conformational defects, or infectious agents.
Pannus or Uberreiter’s disease is a specific, bilateral, progressive, proliferative, chronic, superficial keratitis that begins laterally at the limbus and eventually extends from all quadrants to cover the cornea. It is common in German Shepherds, Belgian Tervurens, Border Collies, Greyhounds, Siberian Huskies, and Australian Shepherds. Specific therapy consists of topical antibiotics, antiviral or antimycotic agents when appropriate, removal of any mechanical irritants, tear replacement when deficient, and corticosteroids or cyclosporin A (or both) when immune-mediated. The latter may need to be continued indefinitely and the frequency varied depending on the response.
Interstitial keratitis is a deep involvement of the corneal stroma that is present with all chronic and many acute cases of anterior uveitis. The corneal vascularization is less branching, finer, and deeper than in superficial keratitis; if the endothelium has been disrupted, corneal edema is often marked. Systemic diseases, such as infectious canine hepatitis, malignant catarrhal fever, systemic mycoses, and septicemias that localize in the eye, can cause bilateral or unilateral interstitial keratitis. Therapy is directed at the anterior uveitis, the systemic infection, or both. A specific, nonulcerative, peripheral, stromal keratitis and persistent anterior uveitis (keratouveitis) occurs in horses; prognosis and response to treatment are poor.
Ulcerative keratitis may be superficial, deep, deep with descemetocele, or perforating. Pain, corneal irregularity, edema, and eventually vascularization are signs of ulceration. A dense, white infiltrate at the ulcer margin indicates strong leukotaxis and bacterial involvement. To detect small ulcers, topical fluorescein may be required. In dogs and horses, most ulcers are mechanical in origin; in cattle, sheep, goats and reindeer, infectious agents and mechanical causes are important; in cats and horses, herpesvirus infection is a frequent cause. All ulcers have the potential for secondary bacterial contamination or endogenous proteinase “melting” of the stroma. Therapy for superficial ulcers is usually medical and consists of topical broad-spectrum antibiotic(s), correction of any mechanical factors, and topical atropine for iridocycloplegia and reduction of ocular pain. Adverse effects of atropine-induced reduced tear production in all species and colic in horses must be considered.
Corneal ulceration, horse
Syndromes of very slow-healing and recurrent superficial ulcers occur in dogs, cats, and horses; in dogs, they may be due to basement membrane disease causing faulty attachment of the corneal epithelium, while in cats and horses, herpesvirus should be suspected. Initial therapy is ulcer debridement followed by topical antibiotics and atropine. For refractory cases in dogs, multiple punctures or cross-hatching (grid and punctate keratotomies) of affected corneas with a 22-gauge needle stimulates most indolent ulcers to heal within 7-10 days. Early reports suggest these keratotomies in cats may predispose to corneal sequestration, and should be employed with great care. Nictitating membrane flaps (or soft contact lenses or collagen shields) act as a pressure bandage and often are therapeutic for shallow ulcers. Medical treatment of deep ulcers is similar to that of superficial ulcers, but many deep ulcers also require conjunctival grafts to strengthen the cornea.
Corneal degeneration and dystrophies occur in dogs, cats, and horses. Corneal degenerations are often unilateral and usually secondary to ocular or systemic diseases. The corneal dystrophies are bilateral, appear inherited or breed-predisposed in dogs, and often consist of triglyceride, cholesterol, and calcium deposits within the corneal stroma. Treatment is not usually necessary.